Many hearing loss patients have some degree of residual hearing in the low frequencies (e.g., below 1 kHz) and a severe hearing loss in the high frequencies (e.g., above 1 kHz). These people cannot benefit from traditional hearing aid amplification because of the severity of the hearing loss in the high frequencies. Nor are they classic cochlear implant candidates, because of their mostly intact low frequency residual hearing.
For this group of people, electro-acoustic stimulation (“EAS”) systems have been developed that provide such patients with the ability to perceive both low and high frequencies. Electro-acoustic stimulation combines the functionality of a hearing aid and a cochlear implant together in the same ear by providing acoustic stimulation representative of low frequency audio content and electrical stimulation representative of high frequency content. The auditory nerve combines the acoustic and electric stimuli into one auditory signal. Results of various studies have shown that electro-acoustic stimulation may enhance speech understanding, pitch discrimination, and music appreciation.
To facilitate electro-acoustic stimulation, a relatively short electrode lead is typically inserted into an EAS patient's cochlea such that electrodes disposed on the lead are located within the region of the cochlea that corresponds to the relatively high frequencies (i.e., the basal region). Unfortunately, however, the EAS patient may lose his or her residual hearing over time. As a result, it may be desirable for an EAS system to represent the low frequency audio content with electrical stimulation instead of with acoustic stimulation. To facilitate such electrical stimulation, the relatively short electrode lead must be replaced with a standard length electrode lead in order to place electrodes in the region of the cochlea that corresponds to the relatively low frequencies (i.e., the apical region).
To avoid the inconvenience, risks, and cost associated with replacing a relatively short electrode lead with a standard length electrode lead, an EAS patient could be fit originally with a standard length electrode lead, assuming the increased insertion depth does not cause damage to the cochlea structures. Electrodes located in the apical region are then disabled to facilitate electro-acoustic stimulation functionality of the EAS system. Unfortunately, biological buildup (e.g., protein buildup and/or buildup of other bodily matter) may accumulate on apical electrodes during extended periods of inactivity (e.g., while acoustic stimulation is still being employed by the EAS system). Such buildup may inhibit current flow through the apical electrodes and thereby render the apical electrodes useless for electrical stimulation when it becomes desirable for the EAS system to represent low frequency audio content with electrical stimulation instead of with acoustic stimulation. Moreover, extended periods of inactivity may result in diminished patency of the hearing nerve cells located in the vicinity of the apical electrodes.